The agricultural industry is facing difficult and challenging times with the increases in the costs of energy and animal production and the associated decline in profitability. This situation leads to pressure to improve profitability by reducing operating costs.
One way of reducing energy costs and energy consumption is by improving how heat is controlled and managed in an animal confinement building. Traditionally in North America, control of heating is simply the use of an “on” or “off” switch. This typically results in increased energy consumption due to overshoot and undershoot. The alternative control approach is “heat to demand.” The amount of heat provided is that required to maintain temperature. It is increased or decreased (i.e., modulated) as needed to maintain temperature. This technology has been developed and applied in European confinement buildings as well as in commercial/industrial products such as boilers and furnaces and has progressed to residential heating applications.
In an agricultural building, such as a swine production building for the farrowing, nursery, finisher, or wean-to-finish grow phases, the environmental conditions are managed by a room temperature controller, i.e. environmental or temperature controller, that controls both heat and ventilation. With these devices, the heat is either “on” or it is “off.” The temperature of the room is typically measured by at least two sensors in the room. As the room temperature rises above the Setpoint used to manage the room conditions, activation of ventilation can occur. On the heat side, if the temperature drops below the Setpoint by a certain amount, heat is activated.
In the example conventional (on/off) ventilation and heat control system shown in FIG. 1, the control logic or philosophy is “not to exceed.” The reference temperature is referred to Daily Required Temperature (DRT); sometimes also referred to as Setpoint. As described below, the control logic does not attempt to maintain or control to the DRT temperature but rather simply to ensure that the DRT is not exceeded. If the actual room temperature starts to go warmer than DRT then the ventilation comes in to play. If the actual room temperature drops sufficiently below DRT the heating system comes in to play. On the ventilation side, there is always a minimum amount of ventilation passing through a swine building to maintain indoor air quality for the animal. This is accomplished either on a continuous rate, where one or more fans may continuously run at partial speed, or it may by conducted on “cycle time,” where it runs at a set rate, e.g., one minute out of four. In addition to the minimum ventilation added to maintain air quality, ventilation can be provided in stages if the room starts to get too warm. This typically is accomplished by using a variable rate fan at, for example, 40 percent capacity, and then ramping it up to full output. If the temperature continues to rise, another variable rate fan can be activated, and so on. Conventional systems include:
(1) Ventilation Mode                a) As actual room temperature exceeds DRT.                    i) Minimum ventilation, typically running at 50% motor speed, the control starts to increase motor speed at DRT+0.1F.                            (a) Typically at DRT+2F the motor is up to 100% speed                                    (i) The +2F is referred to as bandwidth                                                                    ii) If the minimum ventilation fan is at 100% and actual room temperature continues to increase                            (a) A second fan, typically starting at 50% speed starts and ramps up to full speed at DRT+4F                                    iii) If additional stages are required to reduce temperature then they add in as described for the minimum vent/first stage and 2nd stage above            iv) When actual room temperature starts to drop the reverse process occurs, i.e. motors start to ramp down and stages drop out if no longer needed until ultimately ventilation is back to the minimum ventilation settings                        
(2) Heating Mode                a) As actual room temperature drops below DRT −3F, then the heater is turned on                    i) This temperature is typically referred to as the “offset,” i.e. how much it is offset from the DRT            ii) As actual room temperature then starts to increase at DRT−1F the heater is turned off                            (a) The difference between “on” and “off” temperatures is typically referred to as the “differential”                                    iii) The use of “offset” and “differential” is established by the producer based on several parameters including the size of the room and the amount of heat being provided.                            (a) Offsets and differentials are utilized to keep the heat “momentum” being created by the sudden addition of heated air from causing the actual temperature to exceed DRT and start the ventilation cycle which in turn wastes fuel                                    iv) The “Drift” that occurs with conventional systems, typically 5-7 degrees Fahrenheit, is due to the time it takes to start warming the air, during which actual temperature continues to fall, and then stop heating after the heaters are turned off but the temperature continues to rise                        
There are four major integrated room or building control manufacturers in the swine marketplace today providing a 0-10 volts direct current (“vdc”) control outputs for heating control. These controls presently do not contain the necessary control logic capability to properly manage either forced air or radiant modulating heaters. First, an Israel company, Rotem (Petach Tikva, Israel) (see http://www.rotem.com/), produces a “PIGUARD” room controller system (see http://www.rotem.com/pig-farming/superguard_and_piguard), which features temperature and humidity sensors for optimizing environmental control in the pig house industry. Secondly, GSI Electronics (formerly known as Thevco Electronics) (Quebec, Canada) (http://www.thevco.com/corporate.htm), which manufactures management systems for swine, poultry and dairy cows and is sold in the USA as Aerotech or Automated Products devices. Additionally there are products manufactured by Monitrol Inc. (Quebec, Canada) (http://www.monitrolcorp.com/), and Dicam (UK) (http://www.dicamusa.com/).
The technology to create gas-fired heating products that incorporate the ability to function as “heat to demand” or modulating heaters is known. The modulating heaters can be either direct-fired forced air convection heaters or high intensity radiant heaters. To better meet the needs of the market for the future, control manufacturers need to provide appropriate controls with the necessary control logic and outputs to start and control modulating heaters. Additionally, to address the existing installed population of controls a means is needed to integrate with the existing on-off control and modulating heating devices in order to achieve the benefit of variable rate heating.